This invention relates to a so-called form-fill-seal type packaging machine having an improved device for transporting an elongated flexible film material from which bags are to be made by means of a former. More particularly, this invention relates to such a packaging machine capable of effectively straightening the film undergoing a zigzag motion and also of easily retracting a guide roller for the film and the film-straightening device away from the former as well as automatically positioning them near the former.
As shown in FIG. 3, a prior art packaging machine of the form-fill-seal type may be characterized as having a frame 2 which is vertically slidable with respect to a base 7 and a film roll 1 supported by a cantilevered shaft 3 which extends perpendicularly to the front-back direction of the machine. An elongated flexible bag-forming material (hereinafter referred to as a film 4) is pulled out of the film roll 1 and is directed in the forward direction to a former 6 through guide rollers 8, 9 and 32 as well as a dancer roller 10. The former 6 is of a conventional kind, having a skirt-like structure 12 (hereinafter simply referred to as "the skirt") and serving to transform the film 4 into a cylindrical shape. The overlapping side edges of the film are sealed together by means of a vertical sealer 61 to form a tube, and an end sealer 62 is operated to seal the tube at top and bottom positions to form a bag.
Prior art packaging machines thus structured encounter several problems. Firstly, although one of the guide rollers (32) at the downstream end (along the path of travel by the film 4 from the film roll 1 to the former 6) is normally placed adjacent to the skirt 12 so as to be able to guide the film 4 smoothly over to the former 6, it must be removed away from its normal position when the film 4 is initially set or when the former 6 is to be replaced by another of a different kind. Since such removal operations are usually carried out manually, workability of the machine is adversely affected. Secondly, the film 4 must be prevented from moving in a zigzag because its side edge portions should desirably always overlap by the same amount. Although a means is generally provided for straightening the film 4 as it begins to slide transversely to its direction of intended motion, such film-straightening means should be placed as close to the former 6 as possible in order to be effective. If it is too close to the former 6, however, it will stand in the way of the operator when the film 4 is set or the former 6 is exchanged, as mentioned above. Moreover, the film-straightening means will include means for detecting the deviation of the film 4 from its normal course, and this will have the undesirable effect of increasing the number of components of the machine and complicating its structure.
It is therefore a general object of the present invention to eliminate the disadvantages of prior art packaging machines described above by providing a packaging machine with an improved film-transporting device such that its guide roller and film-straightening means can be retracted automatically without requiring the operator's manual operations when the film is initially set or the former is exchanged such that the workability of the machine can be improved. It is a further object of the present invention to accomplish the above without unduly increasing the number of components or the overall size of the machine.